RYE COVER CROP MANAGEMENT IMPACT ON SOIL-WATER CONTENT, SOIL-TEMPERATURE AND SOYBEAN GROWTH

The optimum killing time of a rye (Secale cereale) cover crop is an im portant management decision and can determine the yield of the subsequ ent soybean (Glycine max) crop. The objective of this research was to study a rye cover/soybean system. Soybeans were grown on sandy (Delhi) and loam (Woodstock) soils (1989/1990) with mulch on the soil surface obtained by killing rye approximately 1 and 2 wk before soybean plant ing. A conventional tillage treatment was used as a control. Soil wate r content, soil temperature, rye mulch amount and soybean growth were monitored over the season. Rye mulch amount for the late killing (LK) date was always larger than for the early killing (EK) date. LK decrea sed soil water content at soybean planting time at Delhi in 1989. The rye mulch produced with the LK increased soil water content early in t he soybean growing season in 1990. A substantial decrease in the amoun t of mulch was observed during the growing season and resulted in litt le difference between mulch and no mulch soil water and temperature co nditions later in the season. Extreme temperatures were more frequent under the bare soil, but these were limited to a small percentage of h ours, and did not translate into differences in soybean development ra tes. Reduced soybean growth observed early in the season in one out of four location-years vanished as the season progressed. Number of seed s per pod and nodule number were increased due to rye mulch, but no di fference in soybean yields were observed among treatments.